The present invention relates generally to a magnetoresistive (MR) sensor. More specifically, the present invention relates to an MR read sensor and a method of fabricating the sensor that combines the advantages of abutted junction structure and overlaid structure.
Magnetoresistive (MR) sensors utilize an MR element to read magnetically encoded information from a magnetic medium, such as a disc, by detecting magnetic flux stored on the magnetic medium. An MR sensor must contain both longitudinal bias and transverse bias to maintain the sensor in its optimal operating range so that it can properly detect the magnetic flux. The dual biasing is established through various combinations of magnetic exchange coupling or magnetostatic coupling.
The three critical layers of an MR sensor are the MR element, a spacer material and a soft adjacent layer (SAL). The MR element has magnetoresistive properties and low resistivity and generates an output voltage when a sense current flows through the layer. The SAL is a magnetic bias layer with high resistivity. The SAL biases the magnetization of the MR element and establishes transverse biasing. The spacer material has non-magnetic properties and high resistivity and functions as a spacer between the MR element and SAL. The spacer material helps break the exchange coupling between the MR element and the SAL, which allows the magnetic layers to act as two distinct layers, rather than one strongly coupled layer. Hard-biasing material is placed on each end of the MR sensor, to establish longitudinal biasing and form two passive regions of the sensor. The space between the passive regions maintains the transverse biasing and is referred to as the active region of the sensor.
MR and SAL elements can xe2x80x9cfracturexe2x80x9d into multiple magnetic domains when they are exposed to an external magnetic field. To maximize the stability and output of the MR sensor, it is desirable to maintain the MR and SAL element in a single domain state. Three methods for maintaining the MR and SAL elements in a single domain state are magnetostatic coupling, ferromagnetic exchange coupling and antiferromagnetic exchange coupling. Magnetostatic coupling is accomplished by positioning a permanent magnet adjacent to the MR element. This type of stabilization scheme is known as abutted junction. Exchange coupling is accomplished by depositing a ferromagnetic or antiferromagnetic layer adjacent to the MR layer so that one of the magnetic lattices of the magnetic layer couples with the magnetic lattice of the MR element layer to preserve the single domain state of the sensor. This type of stabilization is referred to as an overlaid structure.
In existing MR sensors, alignment tolerances between various thin film layers and sensor mask features are critical. The alignment tolerances in many prior art MR sensor designs greatly increases the complexity of processing because critical geometries frequently require additional and/or more difficult processing steps. Additional processing steps increase the variance and contamination of the various thin film layers.
For example, designs using continuous MR element and SAL films in both the active and passive areas of the sensor are sensitive to the underlayer of the film. In the passive region of the sensor, the SAL film functions as the underlayer for hard-biasing Cobalt-based alloy films. Cobalt-based hard-biasing films are inherently sensitive to the underlayer crystal texture and to the cleanness and roughness of the SAL/Cobalt-alloy film interface. Also in the passive region, the Cobalt-alloy film fictions as the underlayer for the MR element. The MR element is sensitive to various factors such as the underlayer crystal texture, cleanness and roughness of the Cobalt-alloy film/MR element interface. The dependence of one film to the other makes the process control inherently difficult in fabricating this type of sensor.
In addition, processes involving reactive ion etching or ion milling often require stopping within a very small tolerance, such as 50 Angstroms. These processes leave the surface of the film layer compromised and affect the exchange coupling. The dependence of one film to an adjacent film makes exchange coupling very critical and affects the overall stability of the MR sensor.
One method for simplifying the process of making an MR sensor is by utilizing an abutting magnetoresistive head. The abutted head appears simple with respect to sensor fabrication. Essentially, a thin MR layer extends over the central active region and a hard-magnetic material is formed over the passive regions. The reliability of the sensor, however, is affected by the abutted junctions between the passive and active regions, which introduce complications in the magnetic and electrical properties at these junctions.
Therefore, there is a continuing need for an MR sensor that stabilizes the MR element while reducing the coupling dependence of adjacent films and eliminating the process of reactive ion etching or ion milling. In addition, the MR sensor needs to stabilize the SAL element, yet allow enough rotation of the magnetization so that it can properly bias the MR element.
The present invention is a magnetoresistive (MR) sensor that combines the advantages of abutted junction structure and regular overlaid structure. The abutted junction design is used with the SAL and the overlaid structure is used with the MR element. The abutted junction design uses magnetostatic coupling to stabilize the SAL while allowing the magnetization to rotate. The magnetization must be free to rotate to provide proper magnetostatic coupling between the SAL and MR element. The overlaid structure provides stabilzation to the MR element, but it also eliminates the sensitivity of the abutted junction by laying the MR element adjacent to a hard-biasing film, which allows magnetic exchange coupling. The overlaid structure removes the processing variations usually associated with the abutted junction design. In addition, the combination provides better magnetostatic coupling between the SAL and MR element because the abutted junction design allows more movement of the SAL magnetization, which has a stronger biasing effect on the MR element.
In a second embodiment of the sensor, the hard-biasing film or permanent magnet is separated, to provide the SAL and MR elements with separate hard-biasing films for magnetostatic coupling and magnetic exchange coupling, respectively. The magnetic properties and strength of each permanent magnet can be independently optimized for each of the SAL and MR elements. This allows a more consistent, cleaner and easier to control process, which eliminates variations of permanent magnet properties from sensor to sensor.
A method of making an MR sensor in accordance with the present invention comprises depositing SAL on top of the gap layer and depositing spacer material on top of the SAL. A mask is placed over the central region of the spacer material and SAL. The spacer material and SAL are removed in the areas not covered by the mask. Then, an underlayer material is deposited in the areas where the SAL and spacer material were removed. A hard-biasing material is deposited on top of the underlayer. The mask is removed and the MR element is deposited on top of the spacer material in the active region of the sensor and on top of the hard-biasing material in the passive regions of the sensor. A cap layer is deposited on top of the MR element in the active and passive regions of the sensor. Contacts are placed on top of the cap layer in the passive regions of the sensor.
In a second embodiment of the method, additional material is added to separate the hard-biasing material. A low resistivity material is added after the first hard-biasing material and a second hard-biasing material is deposited on top of the low-resistivity material. The additional materials are deposited before the mask is removed. Once the mask removed, the sensor is built in accordance with the first embodiment.